Flash lamp and ignition means therefor



y 1956 R. M. ANDERSON 2,756,577

FLASH LAMP AND IGNITION MEANS THEREFOR Filed April 7, 1954 100 I I I I I I I I .s 1.0 1.5 a0 as ENERGY MILLIWATT SECONDS 7. LAMPS FLASHED Inventor: Robert M. Anderson, by W a A] His Attorney United States FL'ASH LAlVlP AND IGNITION MEANS THEREFOR Application April 7, 1954, Serial No. 421,509

6 Claims. (CI. 67-31) My invention relates in general to flash lamps of the type used for photographic purposes and comprising a sealed radiation-transmitting bulb in which is enclosed a readily combustible metallic material, together with suitable ignition means therefor, and a combustion-supporting gas filling which, upon ignition of the lamp, enters into a reaction with the combustible material with the resulting emission of a momentary flash of actinic light of high intensity. More particularly, my invention relates to an ignition means for such type flash lamps, and in particular to the composition of the fulminating or primer material thereof. The invention is especially applicable to flash lamps of the type employing substantially pure aluminum, in the form of wire or ribbon such as the socalled shredded foil, as the combustible light-producing material.

.ln flash lamps of the type referred to above, the ignition means customarily comprises a fine tungsten filament connected across the inner ends of the lamp lead-in wires and having at least its end portions, where it is connected to the said wires, embedded in small beads or coatings of a fulminating or primer material coated on the inner ends of the lead-in Wires. To obtain proper synchronization of the light flash from the lamp with the opening of the camera shutter, where the lamp is used for so-called synchronized flash operation such as is common practice at present, it is necessary that the ignition means operate to uniformly ignite all flash lamps alike in order to thereby promote uniform flashing characteristics for the lamp. In addition, it is highly advantageous that the ignition means be operative to ignite and flash the lamp even though the batteries or dry cells employed to supply the electrical current to the lamp to flash it be in a weakened or run-down condition, or even though the resistance of the electrical flashing circuit for the lamp be unduly high due to poor contacts or other causes. To insure the flashing of the lamp under such conditions, therefore, it is advisable to employ an ignition filament having a wire diameter of around 0.6 or 0.7 mil as contrasted to a wire diameter of around 1 mil or so such as has been commonly used in the past, the finer ignition filament, due to its appreciably smaller mass, requiring considerably less electrical power or energy to heat it to the required temperature for igniting the primer material so as to flash the lamp.

The fulminating or primer material which has been found to be most satisfactory for the effective ignition of flash lamps employing pure aluminum, in theform of wire or ribbon such as shredded foil as the combustible material, has been of the composition described and claimed in U. S. Patent No. 2,280,598, G. H. Meridith, issued April 21, 1942, such primer composition consisting of a powder admixture of magnesium, zirconium and potassium perchlorate, in the approximate proportions of 826% magnesium, 42-52% zirconium and 32-40% potassium perchlorate, bonded together by a suitable binder such as a solution of nitrocellulose in amyl acetate. While such composition of primer material has 2,756,577 Patented July 31, 1956 been entirely satisfactory where the ignition filament con sists of a tungsten wire of around 1 mil or so in diameter, it is not sufliciently sensitive for satisfactory use with a finer ignition filament of tungsten wire of around 0.7 mil diameter, a considerable percentage of the lamps in such case failing to flash due to the burn-out of the filament before the primer material has been heated to the required temperature to set it off so as to cause the flashing of the lamp. For manufacturing considerations on the other hand, the primer material should not be so sensitive as to cause so-called lamp flash-outs during the conventional factory glow-testing of the lamps for the presence of air therein, i. e., for the detection of air lamps or leakers, inasmuch as a single lamp flash-out (the ignition and flashing of the lamp by the glow discharge produced therein during the glow-testing operation) temporarily blinds or impairs the vision of the glow-test operator to such an extent as to prevent any further glow-test inspection by such operator for an extended period of time of the order of a half hour or so, thereby necessitating the provision of stand-by glow-test operators so as not to create any interruption in the high-speed productionmanufacture of the flash lamps.

It is an object of my invention, therefore, to provide a flash lamp which is capable of being ignited by the batteries normally employed for such purpose even though they be in a weak or run-down condition, or the resistance of the electrical flashing circuit for the lamp be abnormally high, but which is not subject to being prematurely ignited and flashed by the glow discharged produced in the lamp during the normal factory glow-test thereof for the presence of air therein.

Another object of my invention is to provide an ignition means for a flash lamp which will be operative to ignite and flash the lamp even though the batteries normally employed for such purpose be in a weakened condition or the resistance in the electrical flashing circuit for the lamp be unduly high, but which will not ignite and flash the lamp upon establishment of a glow dischargetherein during the normal factory glow-testing of the lamp for the presence of air therein.

Still another object of my invention is to provide an improved primer composition for the ignition means of a flash lamp which will operate to effectively ignite a flash lamp particularly of the type employing substantially pure aluminum in Wire or ribbon form as the combustible material and which is sufliciently sensitive to be ignited by a tungsten wire ignition filament of around 0.7 mil Wire diameter even when the batteries employed to flash the lamp are in a weakened condition or the resistance in the electrical flashing circuit for the lamp is abnormally high but which is not so sensitive as to be ignited by the glow discharge produced in the lamp during the normal presence of airfactory glow-testing thereof for the therein. 7

Still another object of my invention is to provide a magnesium-containing primer composition for the ignition means of a flash lamp employing a tungsten wire' In accordance with one aspect of the invention, the,

primer material of the ignition means for a flash lamp comprises a powder admixture consisting essentially, by

weight, of approximately 6090% of zirconium, l-8% of magnesium, and 9-35% of potassium perchlorate, bonded together by a suitable binder. In accordance with a further aspect of the invention, an ignition meansfor a flash lamp is constituted by a tungsten wire filament having a wire diameter of the order of 0.7 mil and embedded at least for a part of its length in a primer material of the above-mentioned particular composition.

Further objects and advantages of my invention will appear from the following detaileddescription of a species thereof andfrom the accompanying drawing.

In the drawing, Fig. l is an elevation of a flash lamp comprising my invention;

, Fig. 2 is an enlarged view of the ignition means comprising my invention; and

Fig. 3. is a chart illustrating the flashability, at various energy input levels, of flash lamps according to the invention in comparison with prior type flash lamps.

Referring to Fig. 1, the flash lamp according to the invention comprises a sealed envelope or bulb 1 of glass or other suitable material capable of transmitting the radiations produced Within the bulb upon flashing of the lamp. The bulb 1 contains a loosely distributed filling of combustible material 2 in filamentary form, e. g, fine wireshaving a diameter of less than about 2 mils or finely cut ribbon material such as that commonly known as shredded foil and having a cross-sectional size of theorder of 1 mil or less in width and 1 mil or less in thickness. The combustible material 2 is preferably made of substantially pure aluminum, although other materials such as an aluminum-magnesium alloy containing a small percentage of magnesium, may be employed as Well.

The envelope or bulb 1 also contains a filling of a suitable combustion-supporting gas such as oxygen or an oxygen-containing gas, at a suitable pressure for sup-.

porting the'combustion of the combustible material. The pressure of this gaseous filling will vary depending upon the type of gas employed, the size of the bulb, and the quantity and type of combustible material therein. For bulb sizes commonly in use at present, and with oxygen being used as the combustion-supporting gas and sub stantially pure aluminum as the combustible material, the pressure of the oxygen gas filling will ordinarily vary from around 400 up to as high as 700 mm. of mercury, the higher pressures ordinarily being used in the smaller size lamps. The bulb is coated on its inner or outer surface, or on both surfaces, with coatings of a suitable transparent'varnish or lacquer to thereby prevent crackingof the bulb on charge-flashing and to render the bulb substantially shatterproof.

.Mounted within the bulb 1 within elfective ignition range "of the combustible material 2 therein is alamp ignition means or mount according to the invention comprising an electric energy translation element or small ignition filament 3, preferably in the form of a straight length of tungsten wire, the ends of which are connected to the inner ends of lead-in wires 4, 4 which extend through a glass stem 5 and are connected externally of the bulb to the end eyelet contact 6 and side shell contact 7 of a conventional type base 8 suitably secured to the neck end of the bulb, as by conventional basing cement. The inner ends of the lead-in wires 4, and theportions of the ignition filament 3 at the points of connection thereof to the lead-in wires 4, are coated with a thin film or layer of fulminating substance or primer material 9 to form beads of such material on the said inner ends of the lead-in wires. The fulminating or primer material 9 is applied to the lead-in wires 4 and filament 3 in the form of a paste consisting of extremely sensitive metal powder and a suitable powdered oxidizing agent mixed with a suitable binder.

Heretofore, it has been common practice to employ a tungsten wire ignition filament 3 of around 1 'mil or so in wire diameter. Such size tungsten ignition filaments, however, do not operate to set off the primer material 9 and effect the flashing of the lamp with any degree of consistency when the batteries normally employed for such purpose are in a weakened condition or when the resistance in the electrical flashing circuit for the lamp is abnormally high such as might result from dirty or corroded lamp base or socket contacts. In accordance with the invention, therefore, the ignition filament} is made of finer size tungsten wire having a diameter of the order of 0.7 mil. Such a size ignition filament, because of its appreciably (approximately 50%) smaller cross-sectional area than the 1 mil diameter wire filament heretofore commonly employed, requires considerably less electrical power to heat it to the temperature necessary to ignite the primer material 9. As a result, it will be more apt to ignite the primer material where the electricul power supplied to the filament for lamp ignition purposes is considerably below normal due to the energizing batteries being in a' weakened or run-down condition, or the resistance in the electrical flashing circuit being abnormally high for one reason or another.

As mentioned previously, the primer or fulrninating material 9 which has been found to be most suitable and has been most commonly employed for the ignition of flash lamps of the type employing filamentary combustible material of substantially pure aluminum, has been of the composition disclosed in the aforesaid Meridith Patent 2,280,598 and comprising a. powder admixture of zirconium, magnesium and potasium perchlorate powders bonded together by a suitable binder such as a solution of nitrocellulose in amyl acetate, the powder ingredients being present in the composition in the approximate proportions, by weight, of from 42-52% zirconium, 8-26% magnesium, and 32-40% potassium perchlorate. The presence of magnesium in the primer material is advantageous for several reasons, as disclosed in the above Meridithpatent. It is of particular advantage, however, in that because of its relatively high flame temperature, as compared to zirconium and other like highly sensitive metal powders, the total quantity of primer material 9 required to obtain effective ignitionof the combustible material and proper timing of the flash from the lamp, is considerably smaller than the amount required where no magnesium is present in the primer material. By the use of such a smaller quantity of primer material for the ignition heads 9, the application ofthe primer material to the leadin wires 4 is facilitated and better control over the physical structure, and consequently of the ignition characteristics of the primer coating 9 on each lamp mount, is obtained so that the flash characteristics of the lamps tend to be more uniform than where the primer coatings 9 are of appreciably larger size.

The presence, however, of themagnesium in the primer or fulrninating composition disclosed in the Meridith Patent.2,280,598 ordinarily decreases the heat sensitivity thereof over the case where magnesium is omitted therefrom. Moreover, as the concentration of magnesium in the primer material increases, the more difficult it becomes to ignite such material. For this reason, therefore, While the primer composition of the above-mentioned Meridith patent, containingan appreciable porportion (8-26% by weight) of magnesium, is eminently satisfactory for use in a flash lamp provided with a tungsten wire ignition filament 3 of a size of the order of 1 mil in wire diameter, andwill effectively ignite the lamp inpractically every instance and will insure the proper flashcharacteristics therefor when the batteries employed to flashthelamp are atornear full strength and the resistance in the electrical flashing circuit for the lamp is at anormal level, nevertheless such a relatively high magnesium-content primercomposition is not sufficiently heat sensitive to operate satisfactorily with a finer size tungsten wire ignition filament 3 having a wire diameter of the order of 0.7 mil. In such latter case, the finer ignition filament 3 will, upon energization, frequently heat upandburn out without igniting the primer coatings 9 and flashing the lamp. Such a result obviously would be disconcerting and troublesome to the user ofthe flash lamp,.not only because it may result in the failure to obtain a certain particular picture composition but also becauseitwould often resnltin wastage of film.

In accordance with the invention, I have found that by limiting the content of magnesium in the primer or fulminating composition of the above Meridith patent to an amount no greater than 8%, and increasing the zirconium content to at least of the order of 60% by weight, a primer composition is obtained which, while retaining to a substantial degree all the beneficial ignition characteristics of the previous composition, will in addition possess the added advantage of suificient heat sensitivity to assure its ignition (with resultant flashing of the lamp) in practically every instance by, and before the burn-out of, a tungsten wire ignition filament of around 0.7 mil wire diameter, even though the batteries employed to energize the filament be in a weakened condition or the resistance in the electrical flashing circuit for the lamp be abnormally high. In further accordance with the invention, I have found that the incorporation of at least 1% by weight of magnesium in the primer composition will assure that the heat sensitivity thereof is insufiicient to cause the ignition of the primer heads 9, and resultant premature flash-out of the lamp, by the glow discharge which is produced in the lamp during the conventional factory glow testing thereof for the presence of air in the lamp bulb.

For the purposes of the invention, therefore, the primer or fulminating material employed for the ignition heads 9 of the flash lamp is composed of a powder admixture of the following approximate composition, by weight:

Percent Zirconium powder 60-90 Magnesium powder 1-8 Potassium perchlorate powder 9-35 Percent Zirconium powder 64 Magnesium powder 7.5 Potassium perchlorate powder 28.5

The zirconium, magnesium and potassium perchlorate powders employed in the primer admixture are of extremely fine character, preferably of the order of 325 mesh or finer. The zirconium metal powder preferably is that commercially known as No. 3 grade, manufactured and sold by the Foote Mineral Company of Philadelphia, Pennsylvania, the said No. 3 grade zirconium powder having a relatively high ignition point as compared to other forms of zirconium powders. The magnesium metal powder employed is preferably that manufactured by the United States Magnesium Company of Pleasant Valley, New York, and known as their 325 mesh magnesium powder. Chemically pure (C. P.) grade crystal potassium perchlorate powder is employed as the oxidizing agent in the primer composition.

The primer material is applied to the lead-in wire tips in the form of a paste or suspension of the powder particles in a suitable binder Consisting of around 1% solids and 99% volatile solvents. The subsequent volatilization of the solvents in the binder then leaves a hardened residue 9 composed'almost entirely of the zirconium, magnesium, and potassium perchlorate powder ingredients of the primer paste. The binder preferably employed is a low percentage (i. e., around 2%) solution of nitrocellulose in amyl acetate, such a binder consisting of around 1.2% solids. Enough binder is employed to impart the desired consistency to the primer paste to produce the required size primer beads 9 on the inner lead-in wire tips for a given manufacturing application procedure. Using the above-mentioned specific binder consisting of an approximately 2% solution of nitrocellulose in amyl acetate, the amount of binder solution employed will generally amount to around 18% by weight of the primer paste 6 composition. A specific example of a primer paste composition according to the invention which has been found to be particularly satisfactory is as follows:

Zirconium powder grams 496 Magnesium powder do 58 Potassium perchlorate powder do 223 2% nitrocellulose solution in amyl acetate ml 200 The primer paste material may be prepared in the following manner: the formula quantities of magnesium powder and zirconium powder are first thoroughly mixed with enough of the formula quantity of binder to form a thin paste, the amount of binder required for such purpose being added a few milliliters at a time to the zirconium-magnesium powder admixture and being thoroughly mixed together therewith after each such addition. The remaining portion of the formula quantity of binder is next added, a few milliliters at a time, to the formula quantity of potassium perchlorate powder and thoroughly mixed therewith after each such addition. The potassium perchlorate-binder mixture thus formed is then added to and thoroughly intermixed with the zirconium-magnesium-binder mixture to form the finished primer paste composition.

The increased heat sensitivity of the primer composition according to the invention, and also the greatly increased flashability of the ignition means of my invention, are clearly illustrated by the curves A, B and C in the chart of Fig. 3. These curves show the percentage of lamps of similar construction, except for the ignition means, which will flash for a given input of electrical energy into the ignition filament 3 of the lamp. Curve A depicts the flashability characteristics of flash lamps employing a 1 mil wire diameter tungsten ignition filament 3 and primer beads 9 of a composition conforming to that heretofore generally in use and disclosed and claimed in the aforesaid Meridith Patent No. 2,280,598. Curve B depicts the flashability characteristics of flash lamps employing a 1 mil wire diameter tungsten ignition filament 3 and primer beads 9 of a composition according-to the invention. Curve C depicts the flashability characteristics of flash lamps employing a 0.7 mil wire diameter tungsten ignition filament 3 and primer beads 9 of a composition according to the invention, e. g., the preferred species of the invention comprising approximately 64% of zirconium, 7.5% of magnesium and 28.5% of potassium perchlorate powders. The values upon which the curves A, B and C are based were determined by building up a known electrical charge in a condenser or capacitor and then discharging the said condenser through the ignition filament of the flash lamp.

From a comparison of curves A and C it will be seen that flash lamps according to the invention, employing a 0.7 mil diameter tungsten wire filament with the increased heat-sensitive primer of my invention, require in general only from around 35-50% as much energy input, for the same percentage of lamp flashability, as lamps of the type heretofore in general use and employing a 1 mil diameter tungsten wire filament 3 with the primer composition of the previously mentioned Meridith patent. More particularly, in order to obtain flashability, the lamps according to the invention (curve C) require only about half as much electrical energy input as is required by the lamps heretofore in general use (curve A). Moreover, a comparison of curves A and B shows that as between lamps employing the same size (i. e., 1 mil diameter) tungsten wire filament 3, the lamps provided with the increased heat-sensitive primer composition of my invention (curve B) require from around 15-25% less energy input, for the same percentage of flashability, as lamps provided with the less sensitive primer composition heretofore in general use and conforming to the aforementioned Meridith patent.

From the above comparisons, therefore, it is evident that the use of the primer composition according to the invention effects, of itself, .a marked improvement in lamp flashability, and that when further used in conjunction with a finer (i. e., 0.7 mil diameter) tungsten wire ignition filament than the 1 mil diameter filament heretofore generally in use, a very much greater further improvement in lamp flashability is Obtained. As a result, flash lamps of such construction will flash without difliculty even though the electrical energy supplied to the ignition filament by the energizing batteries and by the flashing circuit be far below the normal level thereof, such as is the case where the batteries are in a weakened or rundown condition or the resistance in the flashing circuit is unduly high due to poor electrical contacts in the circuit.

Of further importance is the fact that the above-mentioned greatly improved lamp flashability characteristics possessed by flash lamps according to the invention are obtained Without causing the percentage of lamp flashouts, on factory glow-testing thereof, to exceed established practical manufacturing limits. Thus, from a high production lamp manufacturing standpoint, the percentage of flash-outs of lamps, on factory glow-test thereof, should not exceed 0.1% in any case. Though the primer composition of my invention is considerably more heatsensitive than that heretofore employed in flash lamps of the type to which the invention appertains and therefore might be expected to cause the percentage of lamp flashouts on glow-testing to exceed the above-mentioned 0.1% limitation, nevertheless I have found that flash lamps according to the invention, provided with the improved higher heat-sensitive primer composition of my invention, definitely possess a lamp flash-out frequency, on conventional factory glow-testing, which is well within the abovementioned 0.1% limitation therefor. In addition, the above-mentioned advantages aflorded by the use of the ignition means according to the invention are obtained without affecting in any noticeable way the flash performance characteristics of the lamp. In other Words, the flash of light produced by the lamp of my invention will have substantially the same intensity andtiming characteristics as that produced by a flash lamp provided with ignition means of the type heretofore in common use as described hereinabove.

Although a preferred embodiment of my invention has been disclosed, it will be understood that the invention is not to be limited to the specific construction and arrangement of parts shown, but that they may be widely modified Within the spirit and scope of my invention as defined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a photoflash lamp, a sealed envelope containing an ignition element including a filament having in heat conducting relation thereto a primer composition comprising a powder admixture consisting essentially of magnesium, zirconium and potassium perchlorate in the approximate proportions by weight of between 1-8% of magnesium, 6090% of zirconium, and 9-35 of potassium perchlorate, said admixture ingredients being bonded together by a suitable binder.

2. In a photoflash lamp, a sealed envelope containing an ignition element including a filament having in heat conducting relation thereto a primer composition comprising a powder admixture consisting essentially of magnesium, zirconium and potassium perchlorate in the approximate proportions, by weight, of the order of 7%% magnesium, 64% zirconium and 28 /2% potassium perchlorate, said admixture ingredients being bonded together by a suitable binder.

3. An igniter for flash lamps comprising a sealed bulb having a pair of lead-in wires sealed thereinto, said igniter comprising an electric energy translation element connected across said lead-in Wires, and coatings of a primer material on said lead-in wires and embedding portions of said filament, said primer material comprising a powder admixture consisting essentially of magnesium, zirconium and. potassium perchlorate in the approximate proportions by weight of between 18% of magnesium, 60-90% of zirconium, and 9-35% of potassium perchlorate, said admixture ingredients being bonded together by a suitable binder.

4. An igniter for flash lamps comprising a sealed bulb having a pair of lead-in Wires sealed thereinto, said igniter comprising a tungsten wire filament having a wire diameter of the order of 0.7 mil and connected across said lead-in wires, and coatings of a primer material on said lead-in wires and embedding portions of said filament, said primer material comprising a powder admixture consisting essentially of magnesium, zirconium and potassium perchlorate in the approximate proportions by weight of between 1-8% of magnesium, 60-90% of zirconium, and 9-35 of potassium perchlorate, said admixture ingredients being bonded together by a suitable binder.

5. A flash lamp comprising a sealed envelope having an oxidizing atmosphere therein, a quantity of filamentary combustible material loosely arranged within said envelope, and ignition means disposed in said envelope within effective ignition range of said combustible material, said ignition means comprising an electric energy translation element at least a portion of which is coated with a fulminating substance, said fulminating substance comprising a powder admixture consisting essentially of magnesium, zirconium and potassium perchlorate in the approximate proportions by weight of between 18% of magnesium, 60-90% of zirconium, and 935% of potassium perchlorate, said admixture ingredients being bonded together by a suitable binder.

6. A flash lamp comprising a sealed envelope having an oxidizing atmosphere therein, a quantity of filamentary combustible material loosely arranged Within said envelope, and ignition means disposed in said envelope within efiective ignition range of said combustible material, said ignition means comprising a tungsten wire filament having a Wire diameter of the order of 0.7 mil and having a portion thereof provided with a coating of a fulminating substance, said fulminating substance comprising a powder admixture consisting essentially of magnesium, zirconium and potassium perchlorate in the approximate proportions by weight of between 1-8% of magnesium, 60-90% of zirconium, and 9-35% of potassium perchlorate, said admixture ingredients being bonded together by a suitable binder.

References Cited in the tile of this patent UNITED STATES PATENTS 

